Specimen slides such as Pap smears are examined by microscope users for specific types of events such as cancer cells. These events are, however, relatively rare and once found are difficult to re-locate for confirmation by others. This is a severe drawback, since an important requirement for cancer screening laboratories is certification by a pathologist, with the need for independent relocation and verification.
Another serious concern with the quality of slide screening, is the nature of the original screening, with a current lack of a positive check on the capability of the screener, and even a lack of quality control feedback for even the most skilled screener. This can and has led to unnecessary deaths, and liability, by reason of missed cell anomalies, resulting in delayed or missed treatment. No reliable and certainly no economical system currently exists for providing requisite slide screening checks as well as checks on screener capability or even a system which provides a quality control feedback to users. The lack of quality control feedback causes even the most skilled screener to operate in a vacuum, without knowledge of what provides proper results in a particular mode of screening.
Methods for re-screening slides are either very crude or entail great economic expense. The prevailing method in aiding relocation is the placement of an ink dot on the slide near the location of the event. This method has proven to be crude, awkward, time consuming and inaccurate. In addition, with this method, it is not possible to ascertain if the entire specimen area of the slide has been uniformly examined or if the areas of the specimen have or have not been scanned. It is accordingly often the case, that if the user is interrupted, it is necessary to restart slide examination. With microscope examination of items, such as diamonds or other types of jewels, for identifying characteristics, the use of ink dots can actually detrimentally mar the appearance of the item.
Ink dot marking and other similar location methods also do not provide any information at all regarding the rate of examination, or time spent at a particular area (important quality control factors). The dots merely function as markers and cannot provide a description of the event or provide any scan history record. As a result of the realization that cancer screening is inaccurate, because areas are missed, there is a major effort underway to improve the quality of screening laboratories by requiring re-screening of randomly selected slides.
Prior art automated screening devices, in the form of motor controlled stage or slide holder devices, generally provide a visible indicia on a slide for observation by the user with coordinates set into the device. The slide is moved in a meander pattern until an event of interest is discovered, at which point the slide is stopped and the position is recorded. While this provides both recording of position and a recording of scan history, it is limited by the need for the user to wait until the event comes into the field of view to stop the meander, rather than by controlling movement by hand. Such devices, besides being very expensive, also interfere with normal use of the microscope and the motion control devices thereof detract from the feel of a normal microscope stage positioning control. Often this detracts from the attention required from the examining screener and a screener can readily "fall asleep" at the lens. Thus, while the physical movement of the screening has been automated, the actual mental assimilation of what is being screened in fact deteriorates.
Very recently, a new device has been developed which utilizes personal computers to record slide data. This device, with video input to specially modified microscopes, superimposes the display of a computer output on the microscope field for viewing by the user. A mouse is used to mark off events of interest. The device is described in Cytometry, vol. 13, pages 109-166 (1992) and Analytical & Quantitative Cytology & Histology, vol. 14, August 1992 and is the basis for the currently marketed HOME device. While useful, such devices are inherently expensive and complex in requiring extensive modification of microscopes (i.e., only HOME supplied microscopes are operative with the system) thereby limiting their utility with respect to different field-available microscopes. As a result, widespread reviewing capability (for both reasons of economics and availability) is severely restricted.
In parent application, Ser. No. 08/089,243 (the disclosure thereof being included herein by reference thereto), the invention therein is described as comprising an economical method end device for use during microscope examination and qualitative control of re-screening of specimens, particularly of specimen slides. The method and device described therein, involve encoding the varying viewing positions on the specimen to correlative computer pixel locations represented by indicia, such as dots, generated by the computer, at pre-selected time intervals. Dots (the exemplified marking indicia), representing varying fields of view, are in turn marked with numbers or symbols indicative of degree of interest of events within the field. Encoding is effected by a mouse or other similar type of encoder which correlates viewing position to specifically correlated location on a screen (as retrieved from computer recordation storage). Retrieval is then easily effected on rescreening by placing the cursor of the computer on a marked event of interest on the screen, by means of movement of the microscope stage, which thereby correlatively positions the lens directly on the event of interest. The area of interest is thus directly viewable under the microscope. A voice record associated with the event may also be made or retrieved in this manner.
In accordance with the method of the parent application, the computer is instructed to and generates time controlled markings, such as dots, which correlate to slide viewing areas on the representative slide image. For example, at time intervals of one second, as regulated by the internal clock of the computer, a dot is generated as being representative of the full area being viewed at that time. As a result, with a subsequent review of the slide, there is a specific correlation of the computer stored dot notation on the representative slide image, directly with an actual original viewed area of the slide. It is thereby also readily ascertainable which areas have and have not been viewed as a function of total specimen area.
A further very useful quality control feature is that the density of dots is a direct indication of the rate at which the slide had been examined. Thus, closely spaced dots indicate a slow scan and widely dispersed dots indicate a more rapid scan.
With the generation of marks, such as dots, each mark (e.g. dot) is further capable of being labelled in turn, such as with a numerical grading, alpha abbreviation, descriptive symbol (predesignated icon) and the like, to inform a reviewer of location of specific events on the examined specimen and their relative importance and/or nature. If desired, a digitized voice record describing the particular events being labelled may also be generated and stored for correlative retrieval upon review of the slide.
In addition to the aforementioned quality control information, it is very useful to also know on a day-to-day and slide-by-slide basis that the slide reviewer or screener is actually giving each specimen "adequate coverage" to locate rare events.
For quality control purposes, "adequate coverage" involves separate parameters of temporal and spatial coverage, but the most useful parameter is a function of both time and space combined. Specifically, it may be useful, but not sufficient, as a measure of screening quality, to (a) record that "x" number of minutes were spent screening a slide, or (b) show that a certain area of the specimen was or was not screened, or even (c) that "y" seconds were spent with the microscope stage at a certain location (factors which were described as being determined by means of the invention of said parent application).
Though these factors may, in and of themselves, give some indication of screening performance, they are of limited value because many minutes may be spent on a small area of the specimen to the exclusion of large areas of possible interest, thus negating the value of the overall length of time spent in reviewing the slide. Furthermore, even a showing that a certain area of the specimen fell under the screener's view does not provide the necessary information that sufficient time was spent looking at that location, to enable a qualified screener to recognize objects or cells of interest.
The manner in which the invention of the parent application is concerned with the laying down of dots as a representation of the field of view in a time-dependent fashion does not however take into account the fact that during rapid screening of a specimen, the amount of time available for viewing any object in the field of view is partly a function of the distance of that object from the center of the field of view. Objects or cells near the outside of the field of view will be seen for only a fraction of the time that cells passing through the center of the field of view are seen. This is based on a screening pattern which is a rapid series of jumps and stops, which constitutes common screening technique, as described in published studies. To compensate for this problem in viewing outlying cells, operators are supposed to screen in overlapping rows or columns (depending upon the screener's preference of movement) so that cells near the outside of the field of view, on one pass of the microscope, get a second chance to be inspected.